With the recent development of mobile devices such as a smart phone and a tablet PC, slimming and thinning of a substrate for a display are required. On the display window or front plate of such a mobile device, glass or tempered glass are generally used as material having excellent mechanical properties. However, glass causes heavy weight of a mobile device due to its own weight, and has a problem of damage by external impact.
Thus, plastic resin is being studied as material that can be used instead of glass. A plastic resin film is light-weighted and has little concern about damage, and thus, is suitable for a tendency to pursue lighter mobile devices. Particularly, in order to achieve a film having high hardness and abrasion resistance, a film in which a hard coating layer consisting of plastic resin is coated on a substrate is being suggested.
As a method for improving the surface hardness of the hard coating layer, increasing the thickness of the hard coating layer may be considered. In order to secure surface hardness to such a level that can be used instead of glass, it is necessary to realize a certain thickness of the hard coating layer. However, as the thickness of the hard coating layer increases, although surface hardness may increase, wrinkles or curls may be increased due to cure shrink of the hard coating layer, and simultaneously, crack or peel of the hard coating layer may be easily generated, and thus, it is not easy to practically apply.
Patent Document 1 discloses a plastic film using binder resin comprising UV curable polyurethane acrylate-based oligomer without monomers. However, the disclosed plastic film has pencil hardness of about 3H, which is not sufficient for replacing a glass panel of a display.
Meanwhile, a display device in which a part of the edge is curved for esthetic, functional reasons, or a display having a generally curved three-dimensional shape is recently receiving attention, and such a tendency is remarkable particularly in mobile devices such as a smart phone, a table PC. However, in case glass is used as a cover plate for protecting such as display of a three-dimensional shape, there is a high risk of damage due to the heavy weight and vulnerablility to external impact of glass.
Although a plastic resin film is light-weighed and has less concern about damage than glass, it is not easy to prepare a film having a three-dimensional structure and exhibiting high hardness of glass level.